1. Field of the Invention
The present invention relates to a field-effect transistor that operates, for example, in a high frequency band.
2. Background Art
National Publication of International Patent Application No. 2009-530857 discloses a field-effect transistor that reduces a peak electric field at a gate edge and corner by reducing a concentration of movable charge in a 2DEG (two-dimensional electron gas). More specifically, a charge reduction region is formed in a region where the two-dimensional electron gas of a channel layer is formed. In a current-carrying state, the charge reduction region has lower conductivity than adjacent regions.
Field-effect transistors to which high voltage is applied have a problem that an electric field is concentrated directly below an end of a gate electrode on a drain electrode side, producing crystal defects. Crystal defects may cause characteristics of the field-effect transistors to deteriorate. It is therefore necessary to reduce the electric field directly below the end of the gate electrode on the drain electrode side.
As the technique disclosed in National Publication of International Patent Application No. 2009-530857, the electric field can be reduced by providing the charge reduction region in the region in which the two-dimensional electron gas is formed. However, providing the charge reduction region in the region in which the two-dimensional electron gas is formed causes the concentration of the two-dimensional electron gas to drastically decrease, resulting in a problem of deteriorating electric characteristics of the field-effect transistor.